1. Field of the Invention
The present invention relates to a toner for developing electrostatic image used for development of a latent image of electrostatics in an electrophotography, an electrostatic recording method, an electrostatic printing process or the like. Particularly, the present invention relates to a toner for developing electrostatic image which has less odor produced upon fixing so as to avoid deteriorating surrounding environment and excellent printing durability. Hereinafter, “a toner for developing electrostatic image” may be simply referred to as “a toner”.
2. Description of the Related Art
Image-forming devices such as an electrophotographic device, an electrostatic recording device, an electrostatic printing device and so on are applied to a copying machine, a printer, a facsimile machine, a complex machine thereof and so on. A method to form a desired image by developing a latent image of electrostatics formed on a photosensitive member with a toner for developing electrostatic image is widely used.
For example, an electrophotographic device using an electrophotography uniformly charges a surface of a photosensitive member generally formed of a photoconductive material with any means used generally, then, a latent image of electrostatics is formed on the photosensitive member. Next, the latent image of electrostatics is developed with the use of a toner. After transferring an image of the toner on a transferring material such as paper or the like, the image is fixed by a method such as heating or the like. Thus, a copy is obtained.
Conventionally, a toner produced by a pulverization method, which is a toner (pulverized toner) obtained by mixing and kneading a binder resin obtained by polymerizing a polymerizable monomer, a colorant and so on followed by pulverizing and classifying, has been generally used. However, the pulverization method has problems of decrease in yield, large energy consumption in pulverization and so on, particularly when producing a toner with a small particle diameter. In order to solve these problems, a toner produced by a polymerization method, a polymerized toner, has been proposed. The polymerized toner are likely to be small in diameter, have uniform form and have narrow size distribution, thus is excellent in printing performance in comparison with pulverized toner.
As a method of producing the polymerized toner, there may be a suspension polymerization method, an emulsion agglomeration method, a dispersion polymerization method and so on. For example, in the suspension polymerization method, firstly, a polymerizable monomer, a colorant, and if required, other additives are mixed to prepare a polymerizable monomer composition, and the polymerizable monomer composition is dispersed in an aqueous dispersion medium containing a dispersion stabilizer followed by agitation with a high-speed agitator or the like to form droplets of the polymerizable monomer composition. Next, the polymerizable monomer composition formed as the droplets is polymerized in the presence of a polymerization initiator followed by washing, filtering, dehydrating and drying, thus, colored resin particles are obtained. Further, the colored resin particles are mixed with an external additive such as an inorganic fine particle or the like to obtain a polymerized toner. If required, the polymerized toner is mixed with a carrier to obtain a two-component developer.
In the above production process of the polymerized toner, some additives added as required disturb polymerization reaction of the polymerizable monomer. An unreacted polymerizable monomer remaining in the toner has been a problem. Also, besides the unreacted polymerizable monomer, it has been a problem that a decomposed product of a polymerization initiator is obtained as a by-product by polymerization using the polymerization initiator and remains in the toner.
If the unreacted polymerizable monomer and the decomposed product of the polymerization initiator remain in the toner, volatiles derived from the unreacted polymerizable monomer and the decomposed product of the polymerization initiator volatilize by heating upon fixing and odor is produced so that surrounding environment is deteriorated. Further, the toners become fusible each other upon storing the toner resulting in blocking, thus causing decrease in shelf stability of the toner and adverse effect on printing performance of the toner.
With respect to the above problem, production of odor upon fixing has been tried to be diminished. For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-321809 suggests a method of producing a toner including a process of stripping treatment under reduced pressure (removal of unreacted polymerizable monomer) with a dispersion liquid containing a colored resin particle after suspension polymerization and discloses t-butylperoxy-2-ethylhexanoate (product name: PERBUTYL O; manufactured by NOF Corporation) as a polymerization initiator.
JP-A No. 2001-117272 suggests a method of producing a toner including a process of stripping treatment under reduced pressure (removal of unreacted polymerizable monomer) and a specific agitation condition with a dispersion liquid containing a colored resin particle after suspension polymerization and discloses t-butylperoxy-isobutylate (product name: PERBUTYL IB; manufactured by NOF Corporation) as a polymerization initiator.
JP-A No. 2000-3076 suggests a method of producing a resin for toner obtained by copolymerizing styrene and (meth) acrylic acid ester using a polymerization initiator and discloses a group consisting of dicinnamoylperoxide and tertiary alkylperoxycinnamate having 4 to 8 carbons as a polymerization initiator.
JP-A No. 2000-321809 and JP-A No. 2001-117272 focus attention on the odor derived from an unreacted polymerizable monomer and try to reduce a residual amount of the unreacted polymerizable monomer remaining in a toner by a stripping treatment under reduced pressure. However, JP-A No. 2000-321809 and JP-A No. 2001-117272 do not focus attention on the odor derived from the decomposed product of the polymerization initiator and do not sufficiently solve the problem of odor. Also, a toner disclosed in JP-A No. 2000-3076 is a pulverized toner obtained by a pulverization method. Since a production process of the toner includes mixing and kneading at high temperature, a residual amount of an unreacted polymerizable monomer remaining in the toner is relatively small, thus odor derived from an unreacted polymerizable monomer produced is considered to be small. However, JP-A No. 2000-3076 does not try to diminish the decomposed product of the polymerization initiator used and the problem of odor is not sufficiently solved. Also, the remaining decomposed product of the polymerization initiator not only produces the odor but also has effect on flowability and charging performance of toner, which causes decrease in printing durability of toner.
In addition to the problem of odor produced upon fixing, a toner is required to be excellent in printing durability so that the toner does not decline printing performance even in continuous printing of plural prints under a severe environment for using a toner such as a high temperature and humidity since use of toner in the area of high temperature and humidity is increasing in recent years. Also, a toner which is excellent in shelf stability at high temperature is required so that toners are not likely to be fusible each other even the toner is left or stored at high temperature.
As there has been such request, it has been necessary to design a toner in which change of charge amount due to environmental changes is small and which can keep a stable charge amount over time and such a toner has been discussed.
For example, JP-A No. Hei. 11 (1999)-15192 discloses a method of producing a toner wherein a polymerizable monomer is subject to suspension polymerization in a suspension medium containing a colorant and an inorganic dispersant in the presence of a quaternary ammonium base containing copolymer comprising a repeating structural unit derived from vinyl aromatic hydrocarbon, a repeating structural unit derived from (meth)acrylate and a repeating structural unit derived from quaternary ammonium base containing (meth)acrylate.
JP-A No. 11 (1999)-15192 is considered to be capable of obtaining a toner which is less likely to be fusible with other toners, can keep a stable charge amount over time to some extent and has shelf stability and printing durability been improved. However, in order to attain high-level requirement of recent years, it is considered that further study is necessary.
An object of the present invention is to provide a toner for developing electrostatic image which has a reduced residual amount of a decomposed product of a polymerization initiator remaining in the toner upon production (mainly an ether component) and an unreacted polymerizable monomer (mainly styrene), less odor produced upon fixing so as to avoid deteriorating surrounding environment, excellent shelf stability at high temperature upon storing or anti-blocking property, and excellent printing durability under both N/N environment and H/H environment upon printing.